Interferon induces a protein kinase that is activated by double-stranded RNA in susceptible cells to phosphorylate the smallest alpha subunit of eukaryotic peptide initiation factor 2 (eIF-2). A different protein kinase specific for eIF-2alpha is activated by heme deficiency in reticulocytes. Both kinases appear to phosphorylate the same sites on eIF-2alpha with concomitant inhibition of protein synthesis, thereby exerting translation control through a common mechanism. Potentially, the state of phosphorylation of eIF-2alpha can be regulated by either protein kinases or phosphatase activity. Components involved in the regulation of both these enzymes will be investigated. For the phosphatase, two heat-stable peptides that each activate the enzyme for different substrates will be studied. The activators will be further characterized with respect to physical properties, interaction with the phosphatase, and the mechanism by which the reticulocyte eIF-2alpha protein kinase is activated and controlled. This kinase may not only be activated by heme deficiency but also in the presence of heme by heat in the order of 40 to 45 degrees. Work will continue on the isolation and characterization of two components, HS and HL, that are involved in this heat-activated system.